Process for making chloroformates with amines as catalysts



a a a c 3,299,114 United States Patent O ce meme,

mobenzyl mercaptan, 4-chloro-l-mercaptonaphthalene,

3,299,114 PROCESS FOR MAKING CHLOROFORMATES WITH AMINES AS CATALYSTS Harry Tilles, El Cerrito, Califi, assignor to Staufier Chemical Company, New York, N.Y., a corporation of Delaware No Drawing. Filed June 10, 1965, Ser. No. 463,005 1 Claim. (Cl. 260-455) This application is a continuation-in-part of my copending application Serial Number 218,161, filed August 20, 1962, now abandoned.

This invention relates in general to an improved method for the preparation of chlorothiolformates.

Various methods are known for the preparation of lower alkyl and phenyl chlorothiolformates, but each of these afford only relatively low yields and impure products. Further, certain known methods require a number of days for completion, require refrigerated cooling and large volumes of reaction mixture, do not afford uniform results (exhibiting sensitivity to reaction conditions), or require the preparation of lead mercaptides.

The present inventors US. Patent No. 3,093,537 discloses the use of activated carbon as a selective catalyst for the following reaction:

Generally, the present invention relates to the process wherein a mixture of the appropriate mercaptan and phosgene are reacted in the presence of a tertiary amine or a nitrogen-containing heterocyclic compound which act as catalyst for the reaction:

RSH+COCl RS( )Cl+HCl wherein R is alkyl, cycloalkyl, lower alkenyl, iaryl, alkaryl, aralkyl, haloaryl, haloarylalkyl, and carboalkoxyalkyl.

As examples of organic mercaptans which can be suitably used in the reaction of the present invention are alkyl mercaptans such as methylrnercaptan, ethylmercaptan, isopropylmercaptan, n-propylmercaptan, isobutylmercaptan, n-butylmercaptan, 2-pentylmercaptan, isoamylmercaptan, n-amylmercaptan, and the like. As

examples of cyclo-alkyl mercaptans the following may be employed: cyclopentylmercaptan, cyclohexylmercaptan, Z-methylcyclohexyl mercaptan, 3-methylcyclohexyl mercaptan, and the like. Allyl mercaptan and butenyl mercaptan are typical examples of lower alkenyl mercaptans that can be used in the above defined reaction. Equally operable are aryl, alkaryl, aralkyl, haloaryl and haloaralkyl compounds exemplified by the following compounds: mercaptobenzene, 2-mercaptonaphthalene, p-mercaptotoluene, o-mercaptotoluene, m-mercaptotoluene, 3,4dimerc aptotoluene, 2,4-dimethylmercaptobenzene, 2, 5-dimethylmercaptobenzene, p tert butylmercaptobenzene, 1-methyl-2-mercaptonaphthalene, 4-ethyl-mercaptobenzene, benzylmercaptan, mercaptoethyl benzene, mercaptopropyl benzene, triphenylmethyl mercaptan, mercaptomethyl naphthalene, mercaptoethyl naphthalene, meroaptobutylnaphthalene, o-chloromercaptobenzene, mchloromercaptobenzene, p-chloromercaptobenzene, 2,5- dichloromercaptobenzene, p-bromomercaptobenzene, o-iodomercaptobenzene, m-iodomercaptobenzene, p-iodomercaptobenzene, o-chlorobenzyl mercaptan, m-chlorobenzyl mercaptan, p-chlorobenzyl mercaptan, 2,4-dichlorobenzyl mercaptan, 3,4-dichlorobenzyl mercaptan, p-bro- 4-bromo-l-mercaptonaphthalene, and the like. Similarly, examples of carboalkoxy-alkyl mercaptans thatcan be reactedv with phosgene according to the present invention are those compounds typified as esters of merc'apto-acids. Suitable examples are methyl mercaptoacetate, ethyl mercaptoacetate, 'propyl mercaptoacetate, butyl mercaptoacetate, pentyl mercaptoacetate, hexyl mercaptoacetate, methyl ot-mercaptopropion-ate, ethyl wmercaptopropionate, pentyl a-mercaptopropionate, methyl fl-mercaptopropionate, ethyl fi-merca'ptopropionate, hexyl /3-mercaptopropionate, methyl u-mercaptobutylrate, propyl a-mercaptobutyrate, hexyl a-rnercaptobutyrate, methyl ,B-mercaptobutyrate, ethyl fl-rnerc-aptobutyrate, hexyl B-mercaptobutyrate, methyl 'y-mercaptobutyrate, ethyl -mercaptobutyrate, hexyl -rnercaptobutyrate, methyl ,B-mercaptovalerate, ethyl B-mercaptovalerate, hexyl fl-mercaptovalerate, methyl a-mercaptovalerate, ethyl e-mercaptovalerate, hexyl 5-mercaptovalerate, and the like.

The catalysts of the present invention are equally useful in the reaction of phosgene and a dithiol and the selectivity of the catalysts isequally effective as activated carbon, both of which are described in detail in the inventor's previously mentioned patent.

The following synthetic methods were used in carrying out the present invention and the tables followinggive the results of such runs.

SYNTHETIC METHOD A A 500 cc. 4-neck flask was provided with stirrer, thermometer, gas inlet tube and Dry Ice condenser. The

' mercaptan and catalyst were charged and then an excess of phosgene was passed in, maintaining the temperature between 20-30 C. with cooling. The time of addition varied between 15 minutes to an hour. After the addition was completed, the reaction mixture was allowed to stir for several hours without any external cooling but the Dry Ice condenser was kept full. Most of the excess phosgene was then stripped out with air at a temperature of 20-30 C. The reaction mixture was washed with 2-100 cc. portions of 4.5% hydrochloric acid and 2-100 cc. portions of water.

After washing, the reaction product was dried over a small amount of anhydrous magnesium sulfate, filtered, and the filtrate was brought to reflux under water pump vacuum in order to remove the volatile impurities. The cooling water in the reflux condenser was maintained at such a temperature that the chlorothiolformate would condense, but the mercaptan would not condense. After the distilland temperature had remained constant for ten minutes, the refluxing was stopped, the yield was obtained and the refractive index of the product was taken.

SYNTHETIC METHOD B This method was the same as A except that the reaction mixture was diluted with -200 cc. of n-pentane before washing. After the washing was completed, and the mixture was dried over anhydrous magnesium sulfate, the n-pentane was removed on the steam bath. This always resulted in some loss by evaporation of the lower alkyl chlorothiolformates. It was then brought to reflux under water pump vacuum.

SYNTHETIC METHOD C This method was the same as B except that the product was vacuum distilled after refluxing under vacuum in order to separate it from high boiling impurities.

Table R1SH+CO C11 RlS-CO CI+HC1 TERTIARY AMINE CATALYST (R2) (Ra)(R4)N Moles of Moles of Moles of Synthesis Yield of 7LD3 of R1 R SH C0 C11 Catalyst Method Chlorothiol- Chlorothiol- R2 R3 R4 formats formate n-C H7 1 .00 1 .20 0.05 78 1 .4755 C211 i-C31'I1 1 .00 1.20 0.05 03 1.4688 C2115 n-C4Ha 1.00 1.22 0 .05 89 1 .4747 C211 t-Cdl 1.00 1122 0.05 48 1.4699 C211 PhenyL 1 .00 1.20 0 .05 72 1.5786 C2115 n-CaH1 1 .00 1 .30 0 .04 85 1 .4753 Phenyl CH CH 11-C3H1 1 .00 1 .30 0 .03 87 1 .4750 Phenyl CzH5 C111 n-C3H1 1.00 1.22 0.02 74 1.4756 11-C6H13 11431111 3... Il'csHm n-CzH-I 1 .00 1.20 0.04 86 1.4755 CzHs CH2CH2CH2CH2CH2 I1-C3H7 l .00 1 .23 0.01. 83 1 .4756 Il-CgH H-CBH17.. Il-CgIIu Table R1SH+COC12 R1S-C-0C1+HC1 HETEROCYOLIC BASIC NITRO GEN COMPOUND CATALYSTS Moles of Moles of Moles 0f Synthesis Yield of nD of B1 RISH (10012 Catalyst Method Chlorothiob Chlorothiol- Catalyst Structure formate formats C 11 1.00 1. 20 0. 06 A 82 1. 4774 Pyndlne N n-CgHr 1. 00 1. 20 0. 06 A 84 1. 4745 Pyridine N l-CQIIT 1.00 1. 20 0.00 A G3 1. 4688 Pyndlne N f 11-04111 1.00 1. 22 0.06 A 89 1.4740 Pyridine N t-CqHp 1. 00 1.22 0. 06 A 18 1. 4096 Pyridine N f 1l-C3lI1j 1.00 1. 20 0. 00 B 75 1. 4727 Pyridine N f Phcnyl 1.00 1. 20 0. 06 C 75 1. 5787 Pyridine 1 11-03117 1.00 1. 20 0. 04 A 88 1. 4748 Quinoline i 11-0311; 1.00 1. 20 0. 01 A s0 1. 4753 Isoquinolinc 1 N 11-03117 1.00 1. 20 0.05 A 76 1. 4752 2-mcthylpyrazinc -CII n-Ca-I'I; 1.00 1. 20 0.07 B 50 1. 4758 Pyrrole 11-0 117 1. 00 1. 20 0. 05 A s0 1. 4750 3-pic01ine 011;

Table-Continued R1sH+ooo12 R1SCOC1+HCl HE'IEROCYCLIC BASIC NITROGEN COMPOUND CATALYSTS Moles of Moles of Moles f Synthesis Yield of nDau of R1 R1SH C001 Catalyst Method Chlorothiol- Chlorothiol- Catalyst Structure formate formate 11-03111 1.00 1. 20 0. 04 A 86 1. 4751 2,4,6-trimethylpyridine CH3 -CH n-CaH-l 1. 00 1. 20 0. A 88 1. 4746 2,4-1utidine n-O3H 1. 00 1. 0. 04 B 74 l. 4751 5-ethyl-2-methyl- C 11 pyridine.

n-C H 1.00 1. 26 0.05 O 78 1. 4750 i-ethylpyridine I 11-03111 1.00 1. 20 0. 04 A 85 1. 4759 2-chl0ro-4,6-dimethy1- N pyrimidine. L

CH Cl In carrying out the process of the present invention, it is advisable that the reaction temperatures be maintained as low as possible, consonant with reasonable reaction rates. As is known, the mercaptans exhibit varying reactivities and this must be taken into account in selecting optimum reaction temperatures.

The process of the present invention is applicable with any ratio of reactants but economics dictate that approximately stoichiometric quantities be employed or, as is the preferred embodiment, a slight excess of phosgene be used.

Therefore, in order to catalyze the process of the present invention any nitrogen containing compound selected from the group consisting of (1) tertiary amines of the formula R3 R2I\LR4 wherein R R and R individually are selected from the group consisting of alkyl and phenyl, or when R is alkyl or phenyl R and R jointly are a divalent alky'lene radical of 4 to 6 carbon atoms, inclusive, and (2) heterocyclic amine compounds selected from the group consisting of pyridines, quinolines, isoquinolines, pyrazines, pyrolles and pyrimidines may be employed.

I claim:

A method for preparing chlorothiolformates comprising reacting a compound selected from the class consisting of alkyl mercaptans, cycloalkyl mercaptans, lower alkenyl mercaptans, aryl mercaptans, alkaryl mercaptans, aralkyl mercaptans, haloaryl mercaptans, haloaralkyl mercaptans and carboalkoxyalkyl mercaptans wit-h phosgene in the 2,370,567 2/1945 Muskat et al 260463 FOREIGN PATENTS 860,063 12/1952 Germany.

OTHER REFERENCES Reimschneider et al.: Monatschefte fiir Chemie, 1953, vol. 84, pp. 518-521.

CHARLES B. PARKER, Primary Examiner.

D. R. MAHANAND, Assistant Examiner. 

